Dampening control circuit for off-set printing apparatus

ABSTRACT

A control circuit for an off-set printing apparatus is described whereby a dampening roll, which is used to wet a printing surface with an ink repelling liquid, is automatically maintained at the proper level of wetness from start-up through completion of the printing operation. A rapid wetting network is employed to quickly wet the dampening roll by rotating a pan roll at a greater than normal speed. An AC liquid impedance signal is generated by applying an AC excitation signal across the dampening roll to sense its liquid impedance and thus the amount of liquid on the dampening roll. An AC amplified liquid impedance signal drives a pair of threshold detectors which respectively recognize a normally dry operating condition and an excessively dry condition of the dampening roll. The output signals of the threshold detectors operate a normal wetting motor and a rapid wetting motor with the latter motor limited in its wetting operation to bring the dampening roll quickly to an acceptable liquid dampening level.

United States Patent [191 [11] 3,822,643 July 9,1974

Mikan et al.

[ DAMPENING CONTROL CIRCUIT FOR OFF-SET PRINTING APPARATUS [75] Inventors: Donald G. Mikan, Ridgefield;

Achille A. Presti, Stamford, both of Conn.

[52] U.S. C1. 101/148 [51] Int. Cl B411 23/04 [58] Field of Search... 101/148, 147, 350, 363-365; 317/246 [56] References Cited UNITED STATES PATENTS 3,191,528 6/1965 Jorgenson l0l/148 3,227,951 1/1966 Dykaor 324/61 3,412,677 11/1968 Kantor 101/148 3,499,383 3/1970 Southam 101/148 3,584,579 6/1971 Rothenberg 101/350 3,688,696 9/1972 Treff 101/350 3,730,086 5/1973 Dauterman 101/148 AC SIGNAL GENERATOR eo c s Primary ExaminerRobert E. Pulfrey Assistant ExaminerEdward M. Coven Attorney, Agent, or Firm-William D. Soltow, Jr.; Albert W. Scribner; Martin D. Wittstein [57] ABSTRACT A control circuit for an off-set printing apparatus is described whereby a dampening roll, which is used to wet a printing surface with an ink repelling liquid, is automatically maintained at the proper level of wetness from start-up through completion of the printing operation. A rapid wetting network is employed to quickly wet the dampening roll by rotating a pan roll at a greater than normal speed. An AC liquid impedance signal is generated by applying an AC excitation signal across the dampening roll to sense its liquid impedance and thus the amount of liquid on the dampening roll. An AC amplified liquid impedance signal drives a pair of threshold detectors which respectively recognize a normally dry operating condition and an excessively dry condition of the dampening roll. The output signals of the threshold detectors operate a normal wetting motor and a rapid wetting motor with the latter motor limited in its wetting operation to bring the dampening roll quickly to an acceptable liquid dampening level.

17 Claims, 2 Drawing Figures DAMPENING CONTROL CIRCUIT FOR OFF-SET PRINTING APPARATUS FIELD OF THE INVENTION This invention relates to an off-set printing apparatus. More specifically, this invention relates to a dampening control circuit used to control the amount of liquid placed on a dampening roll which wets a printing plate in an off-set printing apparatus.

BACKGROUND OF THE INVENTION In a photo off-set lithography press, a printing cylinder carries a curved printing plate which is prepared with fatty or greasy ink receiving areas and water base receiving areas to repel the fatty ink. An ink repelling liquid is applied by a dampening roll whose dampness must be accurately controlled to prevent problems such as wash-out and scumming of the image.

An electrical circuit to control the wetting of a dampening roller in a photo off-set apparatus has been previously described in US. patent to Kantor No. 3,412,677. The control system described in this patent is intended to maintain a liquid balance on the dampening roll for optimum operation of the off-set printing press. An electrical signal representative of the amount of liquid on the dampening roll is used to control an intermediate liquid transferin g roll known as a ductor roll to maintain a desired level of dampness of the dampening roll.

A problem encountered with the apparatus such as described in the aforementioned Kantor patent resides in that the operator of the equipment must adjust the feed of the ink and dampening solution until, in his artisan opinion, the press appears to operate in a satisfactory manner. In other words, the operation of the press from start to finish is not entirely automatic. Such personal attention is not desirable where the operator is not sufficiently qualified to make a high-skilled subjective decision on the printing quality.

The type of wetting solution employed depends upon the nature of the duplicating or off-set process employed. With a wetting agent as described in the aforementioned Kantor patent, an indication of the amount of liquid supplied to the dampening control is obtained with a DC excitation signal. In some other wetting liquids, a DC excitation signal would cause an electrolysis or chemical separation of the liquid components and result in a defective printing process.

SUMMARY OF THE INVENTION In a dampening control circuit for an off-set printing apparatus in accordance with the invention, the amount of liquid on a dampening roll is sensed with an AC operating control circuit. A source of AC signals is connected across detector and oscillator rolls which are in operative contact with a dampening roll. An AC signal representative of the amount of liquid on the dampening roll is then used to control a rapid wetting operation in the event the dampening roll exhibits an excessively dry condition.

Upon sensing of the rapid wet condition, a control is energized to drive a pan roll, which is in contact with the supply of liquid, at a higher speed. The increased speed of the pan roll provides an increased amount of liquid for transfer to the dampening roll which rapidly attains the desired level of wetness. When the AC control signal indicates that the dampening roll is no longer excessively dry, a normal wetting circuit maintains the press and dampening roll supplied with a normal flow of liquid within an allowable range.

The operation of the dampening control circuit in accordance with the invention advantageously enables a completely automatic start-up of the ofi set printing equipment without subjective control over the printing quality. The rapid wetting feature conveniently and accurately brings the off-set printing equipment into acceptable operating conditions. The AC excitation of the dampening roll enables the use of a variety of wetting liquids including those that would, in conventional dampening control circuits, be subjected to undesired electrolysis effects. Electrical smoothing circuits are employed to desensitize the network to mechanical distrubances.

It is, therefore, an object of the invention to provide a dampening control circuit which automatically brings an off-set printing apparatus up to an operating condition. It is a further object of the invention to provide a dampening control circuit for an off-set printing press with which a variety of wetting solutions may be employed to wet the dampening roll.

BRIEF DESCRIPTION OF DRAWINGS These and other objects and advantages of a dampening control circuit in accordance with the invention will be understood from the following description of a preferred embodiment of a control circuit in accordance with the invention, described in conjunction with the drawings wherein FIG. 1 is a block diagram of a dampening control circuit for use in a photo off-set printing apparatus in accordance with the invention; and

FIG. 2 is a schematic representation of a dampening control circuit in accordance with the invention.

DETAILED DESCRIPTION OF EMBODIMENT With reference to FIG. 1, a block diagram of a dampening control circuit 10 is shown for use with a photo off-set printing press (not shown) using a number of dampening elements 12. The off-set printing press includes, as is well-known in the art, a printing cylinder 14 (see FIG. 2) which retains a printing plate 16 in contact with a fatty printing ink supply roll (not shown in FIG. I) and a dampening roll 18 for supplying a water base ink repelling liquid. The off-set printing elements are well-known and reference may be had to the publication of Photo Off-Set Fundamentals by John E. Cogoli, copyrighted 1960 for further description of a photo off-set printing apparatus.

The dampening elements 12 include, as shown in FIG. 2, the dampening roll 18 which is contacted by an v electrically conductive detector roll 20 and an electrically conductive oscillator roll 22 to sense the impedance of the dampening roll 18. The impedance is inversely proportional to the amount of liquid on the dampening roll 18. The impedance of the dampening roll 18 is sensed with an AC excitation signal of constant amplitude from a source 23 and applied across detector roll 20 and oscillator roll 22.

Returning to FIG. 1, the sensed liquid impedance sig nal is applied to an AC amplifier 24 whose amplified output is an AC signal with a magnitude representative of the amount of liquid placed on dampening roll 18. The output of AC amplifier 24 is coupled to a normal wetting detect network 26 which produces on line 28 an output signal for use in controlling the usual running wetting loads of dampening roll 18 through a normal dampening control network 30. Network 36 operates within a range determined by a threshold network whose actuation level is chosen commensurate with a normal running wet condition.

The output of AC amplifier 24 also drives a rapid wetting detect network 32 for controlling the start-up operation of a photo off-set apparatus (not shown). The high level detect network senses an excessively dry condition of dampening roll 18 such as occurs after a long inoperative period.

The output from rapid wetting network 32 is coupled to a rapid wet drive 34 to quickly wet the dampening roll 18 to a level where normal dampening control network 30 may take over. A termination control network 36 is provided to prevent excessive wetting of dampening roll 18 by the rapid wet drive 34.

The dampening control network in accordance with the invention provides a rapid wetting operation which quickly brings dampening roll 18 to the desired normal wetting level. The use of an AC excitation source 23 enables the use of wetting agents that would be disassociated by a DC excitation signal used in conventional dampening control networks.

FIG. 2 shows a more detailed schematic of dampening control circuit 10. AC source 23 produces, on line 40, an AC excitation signal in the form of a square wave which is passed through a DC removal circuit 42 formed of series connected capacitor 44 and potentiometer 46. The AC excitation signal on junction 48 is connected to AC amplifier 24, detector roll and a clamping network 50.

The dampening elements used to wet the dampening roll 18 include, as is conventional in a photo off-set printing press, a supply of liquid 52 to repel the greasy or fatty ink, a pan roll 54 which rotates partially submerged in liquid 52, and a ductor roll 56 which reciprocates between oscillator roll 22 and pan roll 54. The ductor roll 56 is reciprocated by a rotating cam 58 which, in turn, is driven by a non'nal wetting motor 60. A ratchet drive 62, driven by motor 60, is coupled to rotate the drive shaft 63 of pan roll 54 with small incre ments.

In the operation of the photo off-set printing press, the pan roll 54 is operated at a slow ratchet controlled speed to continually take on small quantities of liquid and maintain the pan roll surface wet. Ductor roll 56 is reciprocated between pan roll 54 and oscillator roll 22 to transfer liquid to the latter. As oscillator roll 22 is rotated in response to dampening roll 18, ink repelling liquid is further transferred to dampening roll 18.

The detector and oscillator rolls are made of electrically conductive surface material so that the application of the AC signal at junction 48 is varied in magnitude in proportion to the impedance of the liquid on dampening roll 18.

Clamping network 50 connects junction 48 to ground when a proper clamp signal is applied to input line 64. The effect of clamp network 50 is to inhibit operation of the dampening control network 10 by the AC excitation signal. Clamp network 50 may be, for example, a transistor having its emitter and collector electrodes connected between junction 48 and ground and a base connected to input line 64.

AC amplifier 24 produces a linearly amplified liquid impedance signal on line 28. The amplified liquid impedance signal is greater for higher liquid impedances and thus a drier condition of dampening roll 18 and smaller for a proportionally lower liquid impedance or wetter condition of dampening roll 18.

The linearly amplified AC output is applied to level detection networks 26 and 32 which generate respectively a normal wetting signal on line 66 and a rapid wet signal on line 68. The normal wet signal is generated when a DC voltage proportional to the AC amplified signal on line 28 exceeds a predetermined trigger level of a threshold detector such as zener diode 70. The trigger level or threshold level of zener diode is so selected that it conducts only when the liquid impedance sensed across the dampening roll 18 signifies a normally dry condition.

In a similar manner, the rapid wet signal on line 68 is produced when a DC equivalent of the amplified AC signal on line 28 exceeds a predetermined trigger level of a threshold detector such as zener diode 70'. The threshold level for rendering zener diode 70' conductive is so selected that it only conducts when the liquid impedance of dampening roll 18 signifies an abnormally dry condition, such as during tum-on.

The range of the normal wetting control circuit is thus effectively limited on the wet side by the trigger level of zener diode 70 and on the dry side by the trigger level of zener diode 70' when it conducts in response to an excessively dry condition of the dampening roll 18. The operating range of the rapid wetting control circuit is selected to bring the dampening roll quickly to a level of wetness which is in the operating range of the normal wetting control network 26.

The output 28 of AC amplifier 24 is rectified by a diode 72 and filtered with a capacitor 74 to drive zener threshold detector 70. When the voltage across capacitor 74 and resistor 76 attain the threshold level, zener diode 70 breaks down and current is applied to the base 78 of a normally non-conducting transistor switch 80 to render it conductive. Conduction of transistor 80 effectively brings its collector 82 to ground potential and thus allows normally non-conducting transistor 84 to become conductive by the bias provided to base 86 through resistor 88. Collector 90 of transistor 84 is, in turn, connected to the gate input 92 of an SCR 93 (silicon controlled rectifier) having its cathode 95 coupled, through a coil 94 of a relay 96, to a negative DC supply 98. Hence, when transistor is rendered conductive, SCR 93 is turned on and draws heavy current through coil 94 to close relay switch 100.

Closure of normally open relay switch enables an AC signal on line 102 to deliver a tum-on signal to gate 104 of an AC switch, such as semiconductor AC switch triac 106. Triac 106 couples the AC power to normally wetting motor 60 for as long as the normal dry condition sensed by threshold detector 70 exists. When motor 60 is actuated, ratchet drive 62 incrementally rotates pan roll 54 to wet its surface and cam 58 is rotated to reciprocate ductor roll 56 between pan roll 54 and oscillator roll 22 to deliver ink repelling liquid to dampening roll 18. A ductor roll controlled switch 108 is actuated by the ductor roll and closed when the duotor roll is in a pan-roll-contacting position as shown in dotted line at 110. Switch 108 connects cathode 95 of SCR 93 to ground upon closure of the switch movable pole 112 to extinguish SCR 93 when a gating signal is no longer applied to SCR gate 92.

A rapid wet control for dampening roll 18 is obtained with control circuit 32, which is similar to circuit 26. The threshold detector, however, utilizes a zener diode whose conduction level is so chosen that the zener diode 70' does not conduct until the liquid impedance signifies an excessively dry condition of dampening roll 18. For example, when the dampening roll has not been used for some time and is effectively completely dry, the liquid impedance signal is at a maximum level. This level is sufiiciently high to produce a large DC voltage across capacitor 74' with sufiicient magnitude to render zener diode 70' conductive.

Conduction of diode 70 renders normally olf transistor conductive, which, in turn, drives transistor 84 into conduction. Collector of transistor 84 provides a gating signal to gate 92' of SCR 93 whose conduction causes sufficient current to flow through coil 94' for relay 96' to close switch 100' and a normally open switch in network 36.

Upon closure of switch 100, AC power for a rapid wet motor 122 is allowed to pass through a triac switch 106. The rapid wet motor 122 is coupled through a one-way clutch 124 to drive shaft 63 for pan roll 54. The rapid wet motor operates drive shaft 63 at a greater speed than ratchet drive 62 and overrides the latter to enable pan roll 54 to achieve this increased speed.

When the rapid wet motor 122 has been energized as a result of an excessively dry condition of the dampening roll 18, the large liquid impedance signal on line 28 has also produced an energization of the normal wetting motor 60. Hence, as rapid wetting motor 122 increased the speed of the pan roll 54, the ductor roll 56 is also actuated to transfer the increased moisture on the surface of pan roll 54 to oscillator roll 22 and thus onto dampening roll 18.

The rapid wetting of dampening roll 18 occurs in a short time to reduce the time needed to stabilize the off-set printing process. in order to terminate the rapid wetting operation and prevent excessive wetting of dampening roll 18, control network 36 operates at regular controlled intervals to disengage the rapid wetting operation.

A square wave oscillator 126 produces signals having a frequency selected to prevent excessive wetting of the dampening roll. The square wave pulses on output line 128 are passed through a differentiating network 130 which produces a negative spike output pulse 131 at junction 132. Network 130 includes a series connected capacitor 134, a first diode 136 connected to shunt the positive pulses on junction 138 to ground and a second diode 140 operatively connected between junctions 132 and 138 to allow negative spikes to pass through the momentarily drive normally biased off transistor 140 into conduction.

Collector 142 of transistor 140 is connected to cathode 95' of SCR 93 and emitter 144 is coupled to ground through normally open relay controlled switch 120. Transistor 140 is in parallel with SCR 93 which would normally cease conduction when its power electrodes (the cathode 95 and ground connected anode 97) are electrically shorted by the conduction of transistor 140. However, if a rapid wet signal is still applied to gate 92' of SCR 93', it will continue to conduct when the temporary clamping pulse from control network 36 has passed.

[n the event the rapid wet signal on gate 92 is no longer applied, the control pulse 131 will extinguish conduction of SCR 93' and terminate energization of rapid wetting relay 96' after pulse 131 has passed. When the rapid wet relay 96 has been deenergized, relay switches 100' and 120 are opened to respectively remove the enabling signal for triac 106 and inhibit further conduction of transistor 104. Control network 36 thus regularly provides output pulses to extinguish SCR 93 shortly after the need for rapid wetting has been satisfied.

The frequency of AC signal source 23 for excitation of dampening roll liquid impedance sensing may be 60 cycles. The variation of the liquid impedance is not always entirely a function of the amount of liquid, but includes such factors as bouncing of the detector roll 20 on dampening roll 18 and irregularities in the liquid absorbing cloth with which the dampening roll 18 is covered. The sensitivity of control circuit 10 to such variations of the impedance of the liquid on dampening roll 18 is reduced with a resistor 146 placed in parallel with the liquid impedance sensing rolls 20, 22. Resistor 146 is connected between junction 48 to ground and of such resistance magnitude to adequately reduce the sensitivity.

Amplifier feed-back resistors 148, 150 are selected for an input impedance which is measured in the order of one meg-ohm with a gain of the order of 20. The amplifier 24 is further selected to saturate during excessively dry conditions of dampening roll 18, to limit the voltage swing of the liquid impedance signal at output line 28. Note that capacitors 74-74 are of such size (of the order of 250 pf) to provide further smoothing of the rectified liquid impedance signal and further desensitize the control from high vibrational noise frequencies.

Having thus described a control circuit for automatically bringing an off-set printing press to normal stabilized operation, its advantages may be appreciated. An oeprator need not possess particular subjective training judgment as to the quality of the printed produce. Instead, energization of the apparatus after a long time of inoperation when the dampening roll has had a chance to fully dry out is completely automatic. An excessively dry liquid impedance signal is produced at junction 48 and is sufficient to saturate the amplifier 24. The resulting high rectified liquid impedance signal exceeds the threshold levels of both the normal and rapid wetting control networks 26, 32.

Hence, both normal wetting motor 60 and rapid wetting motor 122 are energized to respectively control the liquid transfering ductor roll 56 and pan roll 54. As the pan roll 54 is rapidly rotated, the dampening roll is quickly brought to its normal operating level of dampness. The liquid impedance signal on line 24 drops below the threshold level of rapid wet control circuit 32 which removes the gating signal from SCR 93. Hence, when the next pulse from oscillator 126 renders transistor 142 conductive, SCR 93' is extinguished and the rapid wetting operation terminated.

The level of the liquid impedance signal on line 28 necessary to achieve termination of the rapid wet control network 32 is chosen so that the normal wet control circuit 26 continues to operate. Thus, normal wetting motor 60 continues to reciprocate ductor roll 56 and advance pan roll 54 through the slower ratchet drive 62. When the liquid impedance signal is further reduced below the threshold level of network 26, the latter ceases to supply a gate signal to SCR 93. Since the mere removal of a gate signal is not sufiicient to extinguish SCR 93, the latter, is rendered non-conductive at such time, following removal of a gate signal, when ductor roll 56 contacts pan roll 54 and causes a closure of switch 108. The ductor roll 56 comes to rest against pan roll 54 until the liquid impedance signal again calls for wetting of dampening roll 18.

The described dampening control circuit 10 may be modified with other circuit elements For example, SCR 93 may be replaced with a transistor of adequate current and voltage carrying capacity so that the SCR extinguishing network 36 may be deleted.

What is claimed is: 1. A dampening control circuit for an olT-set printing machine including means for carrying a printing plate having a printing surface, means for supplying a liquid, a rotatable dampening roll, and apparatus for depositing liquid from the supply means on the dampening roll to wet the printing surface, the control circuit comprismg:

an AC excitation signal source; liquid from the supply means responsive to the AC excitation signal from the source for producing a liquid impedance signal whose magnitude is representative of the amount of liquid on the dampening roll; means responsive to the liquid impedance signal for controlling the amount of liquid on the dampening roll; said controlling means including reference means establishing preselected normal and abnormal wetting demand ranges for the dampening roll which respectively correspond to normally dry and excessively dry conditions of the dampening roll; and said controlling means further including means cooperative with the reference means for producing a normal wetting signal when the liquid impedance signal is within the normal wetting demand range of the dampening roll,

means responsive to the normal wetting signal for controlling said apparatus to maintain the dampening roll in normally wet running condition for liquid wetting of the printing surface, means cooperative with the reference means for producing a rapid wetting signal when the liquid impedance signal is indicative of the preselected excessively dry condition of the dampening roll, and

means actuated by said rapid wetting signal for controlling said apparatus to increase the wetting rate of the dampening roll until said excessively dry condition has been removed.

2. The dampening control circuit as claimed in claim 1, wherein the controlling means includes means for deactivating said means actuated by said rapid wetting signal before excessive wetting of the dampening roll.

3. The dampening control circuit as claimed in claim 2, wherein said deactivating means includes means producing a periodically occuring trigger signal having a frequency of recurrence sleected to be shorter than the time needed to excessively wet the dampening roll after said excessively dry condition of the dampening roll has been removed; and

means actuated by the trigger signal for terminating the operation of the means actuated by said rapid wetting signal.

4. The dampening control circuit as claimed in claim 1, wherein the responsive liquid includes liquid on the dampening roll, and said control circuit includes means for electrically coupling the AC excitation signal to said liquid on the dampening roll to sense a variation of the AC impedance thereof; and

a high input impedance AC amplifier coupled across the coupling means to produce an amplified AC liquid impedance signal.

5. The dampening control circuit as claimed in claim 4 including means for reducing the level of the liquid impedance signal to desensitize the control circuit from noise variations in the liquid impedance signal.

6. The dampening control circuit as claimed in claim 4, wherein the controlling means includes means responsive to the amplifier output for rectifying the amplified AC liquid impedance signal to provide a DC signal whose magnitude is proportional to the impedance of the sensed liquid on dampening roll; and wherein the reference means for producing the normal wetting signal and the rapid wetting signal includes a pair of threshold detectors connected to respectively receive the DC signal, said threshold detectors being selected to respectively sense the occurence of different magnitudes of the DC liquid impedance signal for normal and rapid wetting of the dampening roll.

7. In a dampening control circuit for an off-set printing apparatus having a dampening roll for applying an ink repelling liquid to a printing plate with the liquid being supplied from a rotatable pan roll by a ductor roll moving between the pan roll and an electrically conductive oscillator roll in contact with the dampening roll and with an electrically conductive detector roll being located in contact with the dampening roll, the improvement comprising:

a source of AC signals;

means coupled to the detector and oscillator roll for supplying the AC signals thereto and producing a liquid impedance signal having a magnitude representative of the impedance between the detector and oscillator rolls;

means responsive to the liquid impedance signal for producing a normal wetting signal representative of a normal running range of impedance between the detector and oscillator rolls and further producing a rapid wetting signal representative of an abnormal running range of impedance corresponding to an excessively high range of impedance between the detector and oscillator rolls;

means actuated by the normal wetting signal for controlling the operation of the ductor roll to maintain a desired running dampening condition of the dampening roll; and

means actuated by the rapid wetting signal for increasing the speed of rotation of the pan roll to increase the rate at which the ductor roll supplies liquid from the pan roll to the oscillator roll and thus to the dampening roll in contact with the oscillator roll to establish the desired running dampening condition of the dampening roll.

8. The improved dampening control circuit as claimed in claim 7, wherein the ductor roll controlling means includes first means for rotating the pan roll at a preselected normal running speed to provide a normal supply of liquid for the ductor roll to wet the oscillator roll for normal wetting of the dampening roll; and wherein the pan roll speed increasing means includes a rapid wetting motor coupled to rotate the pan roll at an elevated speed; and a one-way clutch operatively coupled between the first means and the pan roll speed increasing means. 9. The improved dampening control circuit as claimed in claim 7 including pulse generating means coupled to the speed increasing means to terminate operation of the pan roll speed increasing means. 10. The improved dampening control circuit as claimed in claim 8 wherein the control circuit includes pulse generator means for producing pulses at selected intervals corresponding to a maximum allowable time for preventing excessive wetting of the dampening roll; and

means driven by said pulses for inhibiting operation of said pan roll speed increasing means to prevent further rapid wetting of the dampening roll upon removal of the rapid wetting signal.

11. in an off-set printing apparatus having a dampening network to control the amount of liquid transferred to a dampening roll from a pan roll operating in a supply of liquid, the improvement comprising means for producing a dampening signal representative of the amount ofliquid on the dampening roll;

means responsive to a predetermined normal operating range of the dampening signal for maintaining the dampening roll supplied with liquid for a normal running operation of the off-set printing apparatus;

means responsive to the dampening signal for producing a rapid wetting signal when the dampening signal is representative of a preselected excessively dry condition of the dampening roll; and

means actuated by said rapid wetting signal for supplying the dampening roll with liquid at an increased rate until said dampening signal has been returned to said predetermined normal operating range.

12. The improved dampening network as claimed in claim 11, wherein said means for supplying liquid to the dampening roll at an increased rate includes a rapid wetting motor coupled to the pan roll, said rapid wetting motor providing an increase in the rate of rotation of the pan roll to enable it to remove an increased amount of liquid from the supply for transfer to the dampening roll at said increased rate.

13. The improved dampening network as claimed in claim 12 wherein said means for maintaining the dampening roll supplied with liquid for normal running operation includes a normal wetting motor and a ratchet drive driven by the normal wetting motor and coupled to rotate the pan roll, and a one-way clutch operatively coupled between the rotational output of the ratchet drive and the rapid wetting motor, said one-way clutch being operable to prevent rotational drive of the rapid wetting motor by the ratchet drive in the absence of a rapid wetting signal.

14. In a dampening control circuit for an off-set printing apparatus having a dampening roll for applying a liquid to a printing plate with the liquid being transferred from a pan roll by a ductor roll reciprocating be tween the pan roll and an electrically conductive oscillator roll which is in contact with the dampening roll and with an electrically conductive detector roll being located in contact with the dampening roll to enable the sensing of the amount of liquid on the dampening roll, the improvement comprising:

means for producing an excitation signal to generate a liquid dampening signal across the detector and oscillator rolls representative of the amount of liquid on the dampening roll;

means actuated by the liquid dampening signal for controlling the reciprocation of the ductor roll to maintain a normal running wetting range of the dampening roll; and

means actuated by the liquid dampening signal for increasing the available supply of liquid on the pan roll for transfer to the oscillator roll when the liquid dampening signal represents a predetermined excessively dry condition of the dampening control until said normal running wetting range of the dampening roll is achieved.

15. The improved dampening control circuit as claimed in claim 14 wherein the pan roll liquid increasing means includes a rapid wetting motor operatively coupled to rotate the pan roll at a speed selected to increase the available amount of liquid thereon;

means responsive to the liquid dampening signal for producing a rapid wetting signal when the liquid dampening signal signifies an excessively dry condition of the dampening roll; and

means actuated by the rapid wetting signal to energize the rapid wetting motor.

16. The improved dampening control circuit as claimed in claim 15 wherein said wetting motor energizing means includes an SCR having a gate coupled to the rapid wetting signal;

a semiconductor AC switch coupled in series with the rapid wetting motor;

a relay having a relay coil in series connection with the SCR and having a pair of relay controlled switches;

one of the relay controlled switches being coupled to the semiconductor AC switch to energize the motor; and

means including the other relay controlled switch for short circuiting said SCR at predetermined intervals to terminate the energization of the rapid wetting motor.

l7. The improved dampening control circuit as calimed in claim 16 wherein said SCR short circuiting means includes means for producing pulses at regular intervals selected to prevent excessive wetting of the dampening roll by the rapid wetting motor operation;

means actuated by said pulses and connected across the SCR for effectively shorting the power electrodes thereof, said other relay controlled switch being effectively connected to the latter means for effective enabling thereof when the relay is energized by the rapid wetting signal and for inhibiting said latter means when the relay is not energized.

'UNITED STATES PATENT OFFICE CERTH ICATE OF CGRREQTEQN Patent No. 5 v Dated July 9 197 4 I v r( Donald G. Mikan and Achille A'. Presti in the above-identified patent It is certified that error appears corrected as shown below:

and that said Letters Patent are hereby Column 6, Line 10, change "10 to l lO;

Line 12, change oepr'ator" to -operator.

Column 7, Line 63, change Signed and sealed this 11th day of March 1975.

(SEAL) Attest 2 a C. MARSHALL DANN RUTH C. .ASON Commissioner of Patents Attesting Officer and Trademarks "sleected" to -selected. 

1. A dampening control circuit for an off-set printing machine including means for carrying a printing plate having a printing surface, means for supplying a liquid, a rotatable dampening roll, and apparatus for depositing liquid from the supply means on the dampening roll to wet the printing surface, the control circuit comprising: an AC excitation signal source; liquid from the supply means responsive to the AC excitation signal from the source for producing a liquid impedance signal whose magnitude is representative of the amount of liquid on the dampening roll; means responsive to the liquid impedance signal for controlling the amount of liquid on the dampening roll; said controlling means including reference means establishing preselected normal and abnormal wetting demand ranges for the dampening roll which respectively correspond to normally dry and excessively dry conditions of the dampeniNg roll; and said controlling means further including means cooperative with the reference means for producing a normal wetting signal when the liquid impedance signal is within the normal wetting demand range of the dampening roll, means responsive to the normal wetting signal for controlling said apparatus to maintain the dampening roll in normally wet running condition for liquid wetting of the printing surface, means cooperative with the reference means for producing a rapid wetting signal when the liquid impedance signal is indicative of the preselected excessively dry condition of the dampening roll, and means actuated by said rapid wetting signal for controlling said apparatus to increase the wetting rate of the dampening roll until said excessively dry condition has been removed.
 2. The dampening control circuit as claimed in claim 1, wherein the controlling means includes means for deactivating said means actuated by said rapid wetting signal before excessive wetting of the dampening roll.
 3. The dampening control circuit as claimed in claim 2, wherein said deactivating means includes means producing a periodically occuring trigger signal having a frequency of recurrence sleected to be shorter than the time needed to excessively wet the dampening roll after said excessively dry condition of the dampening roll has been removed; and means actuated by the trigger signal for terminating the operation of the means actuated by said rapid wetting signal.
 4. The dampening control circuit as claimed in claim 1, wherein the responsive liquid includes liquid on the dampening roll, and said control circuit includes means for electrically coupling the AC excitation signal to said liquid on the dampening roll to sense a variation of the AC impedance thereof; and a high input impedance AC amplifier coupled across the coupling means to produce an amplified AC liquid impedance signal.
 5. The dampening control circuit as claimed in claim 4 including means for reducing the level of the liquid impedance signal to desensitize the control circuit from noise variations in the liquid impedance signal.
 6. The dampening control circuit as claimed in claim 4, wherein the controlling means includes means responsive to the amplifier output for rectifying the amplified AC liquid impedance signal to provide a DC signal whose magnitude is proportional to the impedance of the sensed liquid on dampening roll; and wherein the reference means for producing the normal wetting signal and the rapid wetting signal includes a pair of threshold detectors connected to respectively receive the DC signal, said threshold detectors being selected to respectively sense the occurence of different magnitudes of the DC liquid impedance signal for normal and rapid wetting of the dampening roll.
 7. In a dampening control circuit for an off-set printing apparatus having a dampening roll for applying an ink repelling liquid to a printing plate with the liquid being supplied from a rotatable pan roll by a ductor roll moving between the pan roll and an electrically conductive oscillator roll in contact with the dampening roll and with an electrically conductive detector roll being located in contact with the dampening roll, the improvement comprising: a source of AC signals; means coupled to the detector and oscillator roll for supplying the AC signals thereto and producing a liquid impedance signal having a magnitude representative of the impedance between the detector and oscillator rolls; means responsive to the liquid impedance signal for producing a normal wetting signal representative of a normal running range of impedance between the detector and oscillator rolls and further producing a rapid wetting signal representative of an abnormal running range of impedance corresponding to an excessively high range of impedance between the detector and oscillator rolls; means actuated by the normal wetting signal for cOntrolling the operation of the ductor roll to maintain a desired running dampening condition of the dampening roll; and means actuated by the rapid wetting signal for increasing the speed of rotation of the pan roll to increase the rate at which the ductor roll supplies liquid from the pan roll to the oscillator roll and thus to the dampening roll in contact with the oscillator roll to establish the desired running dampening condition of the dampening roll.
 8. The improved dampening control circuit as claimed in claim 7, wherein the ductor roll controlling means includes first means for rotating the pan roll at a preselected normal running speed to provide a normal supply of liquid for the ductor roll to wet the oscillator roll for normal wetting of the dampening roll; and wherein the pan roll speed increasing means includes a rapid wetting motor coupled to rotate the pan roll at an elevated speed; and a one-way clutch operatively coupled between the first means and the pan roll speed increasing means.
 9. The improved dampening control circuit as claimed in claim 7 including pulse generating means coupled to the speed increasing means to terminate operation of the pan roll speed increasing means.
 10. The improved dampening control circuit as claimed in claim 8 wherein the control circuit includes pulse generator means for producing pulses at selected intervals corresponding to a maximum allowable time for preventing excessive wetting of the dampening roll; and means driven by said pulses for inhibiting operation of said pan roll speed increasing means to prevent further rapid wetting of the dampening roll upon removal of the rapid wetting signal.
 11. In an off-set printing apparatus having a dampening network to control the amount of liquid transferred to a dampening roll from a pan roll operating in a supply of liquid, the improvement comprising means for producing a dampening signal representative of the amount of liquid on the dampening roll; means responsive to a predetermined normal operating range of the dampening signal for maintaining the dampening roll supplied with liquid for a normal running operation of the off-set printing apparatus; means responsive to the dampening signal for producing a rapid wetting signal when the dampening signal is representative of a preselected excessively dry condition of the dampening roll; and means actuated by said rapid wetting signal for supplying the dampening roll with liquid at an increased rate until said dampening signal has been returned to said predetermined normal operating range.
 12. The improved dampening network as claimed in claim 11, wherein said means for supplying liquid to the dampening roll at an increased rate includes a rapid wetting motor coupled to the pan roll, said rapid wetting motor providing an increase in the rate of rotation of the pan roll to enable it to remove an increased amount of liquid from the supply for transfer to the dampening roll at said increased rate.
 13. The improved dampening network as claimed in claim 12 wherein said means for maintaining the dampening roll supplied with liquid for normal running operation includes a normal wetting motor and a ratchet drive driven by the normal wetting motor and coupled to rotate the pan roll, and a one-way clutch operatively coupled between the rotational output of the ratchet drive and the rapid wetting motor, said one-way clutch being operable to prevent rotational drive of the rapid wetting motor by the ratchet drive in the absence of a rapid wetting signal.
 14. In a dampening control circuit for an off-set printing apparatus having a dampening roll for applying a liquid to a printing plate with the liquid being transferred from a pan roll by a ductor roll reciprocating between the pan roll and an electrically conductive oscillator roll which is in contact with the dampening roll and with an electrically conductive detector roll being located in contact wIth the dampening roll to enable the sensing of the amount of liquid on the dampening roll, the improvement comprising: means for producing an excitation signal to generate a liquid dampening signal across the detector and oscillator rolls representative of the amount of liquid on the dampening roll; means actuated by the liquid dampening signal for controlling the reciprocation of the ductor roll to maintain a normal running wetting range of the dampening roll; and means actuated by the liquid dampening signal for increasing the available supply of liquid on the pan roll for transfer to the oscillator roll when the liquid dampening signal represents a predetermined excessively dry condition of the dampening control until said normal running wetting range of the dampening roll is achieved.
 15. The improved dampening control circuit as claimed in claim 14 wherein the pan roll liquid increasing means includes a rapid wetting motor operatively coupled to rotate the pan roll at a speed selected to increase the available amount of liquid thereon; means responsive to the liquid dampening signal for producing a rapid wetting signal when the liquid dampening signal signifies an excessively dry condition of the dampening roll; and means actuated by the rapid wetting signal to energize the rapid wetting motor.
 16. The improved dampening control circuit as claimed in claim 15 wherein said wetting motor energizing means includes an SCR having a gate coupled to the rapid wetting signal; a semiconductor AC switch coupled in series with the rapid wetting motor; a relay having a relay coil in series connection with the SCR and having a pair of relay controlled switches; one of the relay controlled switches being coupled to the semiconductor AC switch to energize the motor; and means including the other relay controlled switch for short circuiting said SCR at predetermined intervals to terminate the energization of the rapid wetting motor.
 17. The improved dampening control circuit as calimed in claim 16 wherein said SCR short circuiting means includes means for producing pulses at regular intervals selected to prevent excessive wetting of the dampening roll by the rapid wetting motor operation; means actuated by said pulses and connected across the SCR for effectively shorting the power electrodes thereof, said other relay controlled switch being effectively connected to the latter means for effective enabling thereof when the relay is energized by the rapid wetting signal and for inhibiting said latter means when the relay is not energized. 